The present invention relates to an apparatus for processing an original image, such as a copying machine, or facsimile machine, original image memorizing machine.
It is desired in such types of machines that the position or size of an original placed on an original supporting surface be detected. For example, the detection of the original size may be used for automatically selecting the size of recording paper, or it may be compared with the size of recording paper to automatically determine the magnification of the copy. In another type wherein an image of the original is detected by an image pick-up element and converted to the electric signals, which is then reproduced on the photosensitive member surface or the recording material, it is desired that only the information for the area where the original exists is stored, or that the image signal is written in the area corresponding to the size of the original.
As for a simplest and most practical method of detecting the size or position of the original, there is an optical method wherein the original is illuminated, and the light reflected by the original is received by a photosensor, which produces outputs in accordance with the intensity of the received light, so that the outputs are used for determining the position and/or the size of the original.
It is practical to illuminate the original in order to detect or determine the position or the size of the original or to project an image of the original onto the photosensitive member or the image pick-up element. And, it is also practical to provide a original cover for covering the back side of the original to press-contact the original onto the original supporting surface and to prevent the light from going out. Generally, the cover has a white surface adapted to oppose to the back of the original. Then, there is a problem in detecting the position and/or the size of the original, since an original usually has a white background, so that the light reflected by the background of the original and the light reflected by the cover are detected by the photosensor at substantially the same level.
To avoid this problem, it is proposed that the cover be made black or that the cover be opened to uncover the original when the position or the size of the original is detected. By doing so, the light directed to the outside of the original is not incident on the photosensor, so that the light amount is clearly different between the original area and the outside thereof. The clear difference makes possible the detection of the position and/or size.
However, this method has a corresponding problem. Generally speaking, the light incident on the original from the light source is partly reflected by the original surface and partly transmitted therethrough. The ratio of the reflected light and the transmitted light is different depending on the material or the thickness of the original. If there is an additional member at the back of the original as in the case of a book original or in the case of white original cover, the light transmitted through the original is reflected by the additional member and transmitted back through the original to reach the photosensitive member or the image pick-up element and contributes to exposing them to image light. Therefore, in ordinary image processing and image forming machines, the light transmitted through the original and then reflected by the back member is taken into consideration when determining the level of white of the original cover. When, however, the original cover is black, or when it is opened, the light transmitted through the original to the back thereof is absorbed by the black cover or is scattered into the air so that such light is not effective to expose the photosensitive member and the image pick-up element. This decreases the light level for white. High grade paper ordinarily used in offices allows a quite large amount of the light to transmit therethrough. So, the resultant images have foggy background. In the case of tracing paper, a greater amount of light is transmitted and is not returned, so that the background is further black even to such an extent that the image part and the background part are not district from each other. This is not practical.
Therefore, it has been proposed that the covering surface be so colored that the photosensitive member and the image pick-up element are highly sensitive, that is, so that they deem it as white and that an additional sensor which is not sensitive to such a color be used for discriminating the size and position of the originals. The latter sensor is relatively insensitive to the color of the cover, so that the difference between the cover and the original is clear. However, the background of originals is not necessarily white in color. In the case of a non-white background, it becomes difficult to distinguish the original and the cover. Also, it is not possible for such a sensor to double as an image pick-up element.
As a solution to those problems, U.S. Ser. No. 537,679 (corresponding to U.K. Patent Application No. 8327255 and German Patent Application No. 3336961.5) proposes that the covering surface be made of a mirror surface. Since, however, the original cover is handled by operators, the mirror surface can be stained by, for example, a finger print or thumb mark. The mirror surface, having a high rate of specular reflection, e.g., 90-100%, if stained with finger prints or the like, may scatter the light so that the stained portion is erroneously taken as a white portion. Also, the appearance of the surface is bad when it is stained, because it is a mirror surface.